Cis-dichlorodiammine platinum II (DDP), an investigational antitumor agent in clinical trials since 1972, has antitumor activity in genitourinary neoplasms, lymphomas and breast cancer. Renal, hematologic, gastrointestinal and audiologic toxicities have been seen. Recently there have been reports of neurologic toxicity, primarily peripheral neuropathy. In patients treated with cis-platinum at doses of 50 to 100 mg/sq.m every three weeks alone or with other chemotherapeutic agents we have observed sensorimotor polyneuropathies of the hands and feet and cases of papilledema, retrobulbar neuritis and normal pressure hydrocephalus. In some cases, neurologic toxicity has necessitated discontinuance of platinum therapy. Cessation of therapy has resulted in improvement in neurologic symptoms in most cases. Serial nerve conduction studies, prior to and during platinum therapy, have been performed on 10 patients. In 3 patients there has been evidence of a sensory polyneuropathy of axonal type following DDP therapy. Sural nerve biopsy performed on two patients has revealed patterns of axonal degeneration by H and E and electron microscopy studies. However, electron microscopic probe studies and x-ray diffraction analysis have failed to reveal localization of platinum in the nerves. Continued prospective studies on patients receiving platinum, including neutron activation, detection of platinum and further biochemical and histologic studies on nerve biopsies, are planned.